Magnetron



April 1937- G. R. KILGQRE 2,075,855

MAGNETRON Filed Feb. 29, 1936 2 Sheets-Sheet l NVENTOR 6 GE R. KILGOREATTORNEY April 6, 1937. G. R. KILGORE MAGNETRON Filed Feb. 29, 1936 2Sheets-Sheet 2 INVENTOR GEORGE R.| !LGORE w ATTORNEY Patented Apr. 6,1937 UNITED STATES PATENT OFFICE mesne assignments, America, New York,Delaware to Radio Corporation of N. Y., a corporation of ApplicationFebruary 29, 1936, Serial No. 66,379

Claims.

My invention relates to electron discharge devices for use at highfrequencies, more particularly to improvements in devices of theso-called magnetron type in which the electrode system is 5 positionedwithin a magnetic field.

The conventional magnetron comprises a straight thermionic cathode,usually in the form of a filament, an anode coaxial with and surroundingthe thermionic cathode and a magnet 1() for producing a strong magneticfield parallel to the cathode. The anode, which may be of themulti-segment type, is usually the so-called split anode with twosemi-cylindrical sections.

The magnetron tube is particularly useful at 5 very high frequencies,that is, frequencies of the order of 300 megacycles and higher. In orderto function at these high frequencies the tubes must have very smallelectrodes. It is difiicult to provide for such tubes an externalcircuit which will 0 have inductance and capacity low enough to respondto the higher frequencies at which the tube can operate. One partialsolution of this prob lem is to use internal circuit magnetrons, inwhich the oscillator circuit comprises a loop of wire inside the tubeenvelope and connected directly to the electrode system. Such amagnetron and its associated circuit will function at high frequencies,but the power output is limited to only a few watts by the heatgenerated during operation of the tube. Blackening or roughening thesurface,

for example, of the anode increases the heat dissipation of a tube, butis of little practical effect with small anodes, and also increases thehigh frequency resistance of the anode because substantially all of thehigh frequency currents flow on the surface. Another difficultyencountered in magnetron tubes with glass envelopes is the softening ofthe glass near the ends of the anode and cathode due to theconcentration of the electrons on the glass envelope at these points.

It is an object of my invention to provide an improved electrondischarge device of the magnetron type operable at ultra-highfrequencies and having a comparatively high power output. An-

other object of my invention is to provide such a high power magnetronin which the softening of the glass envelope adjacent the ends of theoathode and anode is eliminated.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawings in whichFigure 1 is a v perspective view with parts broken away of an electrondischarge device of the magnetron type embodying my invention; Figure 2is an enlarged longitudinal section of the upper part of Figure 1;Figure 3 is a transverse section taken along the line 3-3 of Figure 2;Figures 4, 5 and. 6 show modifications of my invention.

The preferred embodiment of my invention, shown in Figures 1, 2 and 3,is a magnetron of the split anode type which comprises an evacuatedenvelope [0 provided with a conventional base II and press l2. Theelectrode assembly is supported on the press by a pair of lead andsupport wires i3. In accordance with my invention the electrode assemblyis provided with a directly connected internal circuit and comprises aU-shaped member I 4, preferably of copper, having semicylindrical legsI5 having a large heat absorbing capacity, the inside facing surfaces ofwhich are flat and parallel. The heat radiation of these legs isincreased by a black coating [6, preferably carbon, on only theiroutside surfaces, as shown in the drawing. Preferably no coating isapplied along the margin ll adjacent the inside sur faces of the legsIS. The lower free ends of the U- shaped member M are provided withinwardly extending portions l8 having oppositely disposedsemi-cylindrical surfaces providing a central circular bore 19. Thesetwo extensions constitute the anode segments of the split anodemagnetron. The U-shaped portion constitutes the internal circuitdirectly connected to the two segments of the anode. The legs of theU-shaped member can be considered as elongated parallel extensions ofthe anode segments and as electrically connected at the ends remote fromthe anode segments to provide an internal circuit. A straight thermioniccathode 20, preferably a heavy filament, is supported axially of thecentral bore or cylindrical chamber [9 on the leads [3, as best shown inFigure 2. A pair of shields 2|, also supported on and electricallyconnected to the leads I3 adjacent the anode at the opposite ends of theoathode, shield the glass envelope [0 from the electrons which wouldotherwise be concentrated on it. These shields are preferably ofnon-magnetic metal, such as molybdenum, so as not to interfere with themagnetic field which is induced parallel to the cathode during operationof the tube. On each of the lower free ends of the legs l5 of theU-shaped member [4 is a support comprising a heavy wire or rod 22 and asmaller wire 23 fused into a member 24 of glass or ceramic materialcarried on the lead wires [3. The wires 23 may be connected to pins inthe base to serve as a connection to external transmission lines, orthey may terminate as shown in Figure 2, just below the mica spacer 21.Other methods may then be employed to couple the internal circuit to thetransmission lines. The U-shaped member I4 is o electrically connectedat the top to a flexible lead 25 to provide a voltage connection for theanodes at the lower end of the U-shaped member M. This flexible leadalso allows expansion and con traction of the electrodes duringoperation of the i tube. The bottom lead i3 could be made flexibleinstead of the top lead 25. The mount is spaced from the walls of thetube envelope at the upper end by the mica spacer 26 secured to theU-shaped member l4 and at the lower end by the mica spacer 2! supportedon the lead and support wires E3, the edges of the spacers contactingthe wall of the envelope of the tube. Electro-magnets 28 positioned atopposite ends of the cathode on the outside of the envelope provide astrong magnetic field longitudinal of the cathode during operation ofthe tube.

The conventional internal circuit member used with a magnetron comprisesa wire loop connected to the anode segments. The heat dissipation by aswell as heat conduction from the anodes is very limited inasmuch as theanode surfaces are of small area and the internal wire loop is of smallcross section as well as small area. Blackening the surfaces of theanode segments is in- 00 effective because the surfaces are too small tora-- diate and thus dissipate much heat. Roughening or blackening thewire loop of the internal circuit member is objectionable because theresistance of the wire surfaces to high frequency current which flowmainly on and near the surfaces of the conductors is increased, thusincreasing the power losses in the magnetron. I have solved both theproblem of heat conduction from the anode segments and heat dissipationto increase 0 the power output of a magnetron by my invention, at thesame time decreasing the resistance to the flow of high frequencycurrents.

The legs [5 of the U-shaped member l4 have a large area and transversecross section, one of their dimensions being preferably as great as theanode segments themselves. These legs have a large mass in comparisonwith the anode segments. As heat developed at the internal surfaces ofthe anode segments is quickly conducted away and dissipated by the legsI5, the anode segments are kept comparatively cool. While the legsnaturally dissipate heat by radiation, I make them much more efficientradiators by roughening and coating them with carbon. While thisroughening and coating with carbon increases the emissivity of theinternal circuit portion of the magnetron, it increases the highfrequency resistance at its surface to the flow of high frequencycurrents and in the ordinary loop type of circuit would reduce themaximum output of the tube. In accordance with my invention I provide alarge conducting surface of comparatively low high frequency resistancefor the high frequency currents by forming the legs 55 with large flatparallel surfaces of a width corresponding to the length of the anodesegments. In this way the resistance of the internal circuit is reducedand the current density is decreased over that in the conventional loopwire so that the generated heat is decreased. These inside surfaces anda slight margin on the outside of the legs near these flat surfaces arenot coated with carbon. At the same time I obtain the advantage of beingable to rapidly conduct the heat away from the surfaces carrying thehigh frequency currents and dissipate it through the envelope of thetube. By making a magnetron tube in accordance with my invention I havebeen able to increase the output of the tube to from a few watts output,which is the output of the conventional magnetron, to 50 watts output ata wave length of 60 centimeters with an emciency greater than thirtypercent. The shields iii are effective in preventing the elec tronswhich pass the ends of the anode from bombarding the glass. Thisbombardment is particularly bad in magnetrons because of the focusingeffect of the magnetic field.

The principal advantages of a magnetron made in accordance with myinvention are: a decrease in resistance, increased heat conduction fromthe tube elements, increased radiating surface, a reduction ofdielectric losses and a circuit which will tune to higher frequenciesthan theexternal circuit type of magnetron. While shown as applied to amagnetron, my invention is equally applicable to other types of tubes inwhich it is desired to have a large power output at high frequencies.

In Figure 4 I show modified form of magnetron made in accordance with myinvention in which the upper end of the envelope has been replaced by ametal cup-shaped member 30 secured to the internal circuit element [4,for example, by welding, and fused to the glass envelope ID to providean envelope for the tube elements. The cup-shaped member 30 could bemade integral with the member Id. The member 30 can be used as theconnecting element and also acts as an external heat radiator for theend of the internal circuit element (4.

In the past water cooling of the anode of a magnetron has not beenfeasible due to the small size of the anode or anode segments and thecomplications introduced by sealing the intake and exhaust tubes of thecooling system in the glass envelope which construction introducesstresses in the glass envelope at the seals due to temperaturedifferentials of the cooling medium and glass envelope. My invention hasmade it possible to overcome these difficulties and use water cooling toadvantage.

In the modification shown in Figure 5 a metal tubular member 32 closedat one end is secured to the circuit element M by a screw member 33, thelip of the tubular member 32 being sealed to the glass envelope If! toclose the end of the envelope. A water cooling jacket 34 is secured tothe member 33 and is provided with an in-take 35 and an exhaust 36. Theheat is both radiated from the surface of the legs 15 to the walls ofthe tubular member 32 as well as conducted to the metallic member 32through the ends of the circuit element M. This heat of course isabsorbed and carried out by the cooling fluid passed through the waterjacket 34. In this modification the internal circuit is connected to thetransmission lines by means of the anode leads 23.

In Figure 6 I show a modification of the electron shield for the glassenvelope. This modification comprises a cylindrical member 35 supportedagainst the glass wall of the envelope It]. It may be coated on the wallof the envelope.

' A magnetron made in accordance with my invention is simple andeffective and capable of large power outputs due to the novelconstruction of the anodes and internal circuit member. While I haveshown the anodes and internal circuit member as formed from a coppercylinder, it is apparent that the anodes and the internal circuit membercould be made in various other ways; for example, by forming the anodesand legs separately and securing them together and properly spacing themby means of another member at the ends of the legs opposite from theends carrying the anode segments.

While I have indicated the preferred embodiment of my invention of whichI am now aware and have also indicated only one specific application forwhich my invention may be employed, it will be apparent that myinvention is by no means limited to the exact forms illustrated or theuse indicated, but that many variations may be made in the particularstructure used and the purpose for which it is employed withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim as new is:

1. A magnetron having an envelope containing an elongated U-shapedmember, the legs of which have a comparatively large transverse crosssection and are of comparatively large mass, the inner facing surfacesof said legs being closely spaced, fiat and parallel, a pair of anodesegments at the free ends of said legs on the inside surfaces thereofand having oppositelydisposed semi-cylindrical surfaces providing acylindrical chamber the axis of which is parallel to the flat surfacesof the legs of said U-shaped member, a straight thermionic cathodepositioned axially of said cylindrical chamber and means for inducing amagnetic field longitudinally of said cathode.

2. A magnetron having an envelope containing a pair of anode segmentshaving oppositely disposed semi-cylindrical surfaces forming acylindrical chamber, each of said anodes being provided with anelongated extension, said extensions being parallel and electricallyconnected at the ends remote from said anodes to provide a U-shapedinternal circuit connected to said anode segments, the facing surfacesof the extensions opposed to each other being fiat and parallel and of awidth co-extensive with the length of said anodes, said extensionshaving comparatively thick transverse cross sections in comparison withsaid anodes, a straight thermionic cathode disposed axially of saidanode segments and means for inducing a magnetic field longitudinally ofsaid cathode.

3. A magnetron having a tubular envelope containing a longitudinallyextending U-shaped member, the legs of which have a comparatively largetransverse cross section of semi-cylindrical form, the facing surfacesof the legs being fiat and parallel, anode extensions at the free end ofsaid legs on the facing surface thereof provided with oppositelydisposed semi-cylindrical surfaces forming a cylindrical chamberextending parallel to and co-extensive with the fiat surfaces of saidlegs, a blackened coating on the semi-cylindrical surfaces of said legsto increase the heat emissivity of said legs, a straight thermioniccathode positioned axially of the cylindrical chamber and means forproducing a magnetic field longitudinally of said cathode.

4. A magnetron having a tubular envelope containing a longitudinallyextending U-shaped member, the legs of which have a comparatively largetransverse cross section of semi-cylindrical form, the inner facingsurfaces of the legs being flat and parallel, the anode extensions atthe free ends of said legs on the inside surface thereof provided withoppositely disposed semicylindrical surfaces forming a cylindricalchamber extending parallel to and co-extensive with the flat surfaces ofsaid legs, a blackened coating on the semi-cylindrical surfaces of saidlegs to increase the heat emissivity of said legs, a straight thermioniccathode positioned axially of said cylindrical chamber, means forproducing a magnetic field longitudinally of said cathode, andnon-magnetic shields positioned between the ends of the anode segmentsand the envelope of the tube at opposite ends of said straightthermionic cathode.

5. A magnetron having an elongated envelope closed at one end with atubular metal member and containing an elongated U-shaped member, thelegs of which have a comparatively large transverse cross section andare of comparatively large mass, the inner facing surfaces of said legsbeing closely spaced, flat and parallel, a pair of anode segments at thefree end of said legs on the inside surfaces and having oppositelydisposed semi-cylindrical surfaces providing a cylindrical chamber, theaxis of which is parallel to the fiat surfaces of the legs of saidU-shaped member, a straight thermionic cathode positioned axially ofsaid cylindrical chamber and means for producing a magnetic fieldlongitudinally of said cathode, the end of said U-shaped member oppositefrom said anode segments being Within and secured to said tubular metalmember, and a cooling jacket surrounding said tubular metal member.

GEORGE R. KILGORE.

